Hi Ben,
Many thanks for the comprehensive explanation, however.....
In the case of the Seagate Backup drives, their own backup software does NOT work on Windows Server. I called Seagate themselves and confirmed this. Moreover, you absolutely cannot reformat those drives with a 512 byte sector size.
But, Windows Server will ONLY backup to 512 byte sectors.
Moreover, when set you up backup to a new drive, even one that already formatted, it insists on re-formatting the destination drive.
And to add insult to injury, I've not been able to find out what sector sizes are supported on any drives I've looked at so far on any major drive manufacturer's web site.
So I'm now between a rock and a hard place.
George.
-----Original Message-----
From: Blind-sysadmins [mailto:blind-sysadmins-bounces@lists.hodgsonfamily.org] On Behalf Of Ben Mustill-Rose
Sent: 26 June 2014 13:32
To: Blind sysadmins list
Subject: Re: [Blind-sysadmins] USB External Server Backup Drives
Hi,
This is an interesting one; I sell hard drives so I have to deal with this sort of thing every now and again. I'll try and give some background to the problem below:
Traditionally, hard drives have had a sector size of 512 bytes. This worked well for a long time, but it's not really optimum for larger sized drives. This is mainly due to ECC data - there are other pieces of information stored in sectors, but ECC is probably the most well-known so I'll stick to talking about ECC in this email. Each sector has a certain amount of bytes reserved for ECC, so on larger drives, the amount of capacity that is reserved for ECC really starts to add up.
To solve this, hard drive manufacturers shifted to a 4K sector size instead. If the same ECC algorithms are used, to put it simply, much less space is taken up by ECC due to there being fewer sectors on the drive - 4096 / 512 = 8, so in theory 8 times less.
To try and ease the transition, manufacturers introduced what are known as advanced format or AF drives where the physical sector size is 4K but for compatibility reasons, the drive will usually (more on this later) show a sector size of 512B to the OS. Unfortunately, just to make things a bit more confusing, there are a *very* small number of drives available now that don't perform the 512B emulation - E.G.
they expose 4K sectors to the OS by default, but these drives are also labelled as advanced format drives.
The problem (in fairly simplistic terms) is that most applications only deal with logical sectors, so sometimes write operations will fail. Let’s suppose that some form of application exists that stores data in 512B "chunks" due to it being written before 4K sectors were introduced. On a drive that has physical 4K but emulates 512B, 8 "chunks" of data will be stored per physical sector. Unfortunately, if some form of corruption were to happen, potentially 8 "chunks" of data are now lost instead of one.
I'm not sure how the backup program you're using works, but imho the problem probably relates to it assuming 512B physical sectors but due to the API method it's using to write files*, on drives that have physical 4K but emulate 512B it's getting confused. *There are multiple API methods to handle reads & writes; some return the logical sector size but some return the physical size, so compatibility will depend on what method is used.
The best root to go would be for you to make your own external - E.G.
buy a drive & a USB enclosure so that you can be sure that the drive you're using is 512B physical. Any Western Digital drive with an "a"
as the second character of the block of 4 letters after the numbers will be 512B physical - for example, some 2TB drives that should work are WD20EACS, WD20EADS, WD20EARS, WD20EACX, WD20EADX and WD20EARX.
Anything with a z instead of an a is physical 4K with 512B emulation - E.G. WD20EZRX won't work.
Hope this helps.
Cheers,
Ben.
On 6/26/14, Andrew Hodgson
Aha,
I used 1TB drives on SBS as it compressed everything so I could get quite a few incrementals on it.
It looks like Western Digital have a solution to this problem:
http://wdc.custhelp.com/app/answers/detail/a_id/6618
Not sure whether you can do something similar in Seagate drives.
Andrew.
-----Original Message----- From: Blind-sysadmins [mailto:blind-sysadmins-bounces@lists.hodgsonfamily.org] On Behalf Of George Bell Sent: 26 June 2014 11:06 To: Blind sysadmins list Subject: Re: [Blind-sysadmins] USB External Server Backup Drives
Total on all drives is around 800 GB, so I'd figured that 2 TB would allow for that plus incrementals.
Up until now, I'd been using a 300 GB Maxstor USB drive, and just backing up the System, not the data.
This is a known issue, and below I've pasted just one easy to understand explanation.
Allegedly some of these larger drives do support 512k sector size, but it's all but impossible to find out which. Hence my asking if anyone was currently using one and what make and mode.
George.
"The reason is that most of these large drives have a 4K sector size, rather than the older 512 byte sector size. You can get a patch for Windows 7 and Windows Server 2008 R2 that fixes most problems, but it does not fix the backup issue.
The further reason is that Windows Server Backup uses VHD virtual drives as its file format. The VHD format presumes the use of 512byte sectors, and the drivers that read and write data are optimised for this. You cannot create or mount VHDs on a disk with 4K sectors."
-----Original Message----- From: Blind-sysadmins [mailto:blind-sysadmins-bounces@lists.hodgsonfamily.org] On Behalf Of Andrew Hodgson Sent: 26 June 2014 10:04 To: Blind sysadmins list Subject: Re: [Blind-sysadmins] USB External Server Backup Drives
Hi,
How much data are you backing up? I used standard USB drives and they worked fine.
Andrew.
-----Original Message----- From: Blind-sysadmins [mailto:blind-sysadmins-bounces@lists.hodgsonfamily.org] On Behalf Of George Bell Sent: 26 June 2014 09:56 To: Blind sysadmins list Subject: [Blind-sysadmins] USB External Server Backup Drives
Does anyone know of, and perhaps even use, a make and model of UEB external drive which will allow backup of SBS 2011/Server 2008 R2. Ideally I need 2.
There appears to be a very limited range of such drives, and certainly the likes of the Seagate Backup Plus (2 TB) do not work.
It needs to be something I can remove one from the premises, without getting a hernia in the process.
George. _______________________________________________ Blind-sysadmins mailing list Blind-sysadmins@lists.hodgsonfamily.org http://lists.hodgsonfamily.org/listinfo/blind-sysadmins
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